Convective arc stabilization by lamp rotation

ABSTRACT

A constricted arc-discharge device having means for physically rotating the arc-tube about the longitudinal axis of the arc-tube to stabilize and maintain the constricted arc proximate the longitudinal axis of the arc tube. This device thereby avoids problems caused by arc bowing of the constricted arc-discharge. The device operates with a discharge sustaining filling comprising mercury and metallic halide and provides an extremely efficient source of visible radiation.

United States Patent Walter J. Buruham Pittsburgh;

Robert J. Zollweg, Monroevllle, both of, Pa. 794,202

Jan. 27, 1969 June 29, 1971 Westinghouse Electric Corporation Pittsburgh, Pa.

Inventors Appl. No Filed Patented Assignee CONVECT IVE ARC STABILIZATION BY LAMP ROTATION 1 Claim, 4 Drawing Figs.

[1.8. CI. 313/148, 313/17, 313/149, 313/184, 313/204, 313/220 1111.01 H01j 1/52, HOlj 61/30 Field oiSeareh 313/147,

[56] References Cited UNITED STATES PATENTS 2,004,175 6/1935 Schottky 1. 313/204 2,111,412 3/1938 Ungelenk 313/149X 2,924,733 2/1960 Schirmer et al... 313/220X 3,076,377 2/1963 Brownscombe 240/49 X 3,426,233 2/1969 Simon etal. 313/149 X 3,450,925 6/1969 Johnson 313/184 X Primary Examiner.lohn Kominski Assistant Examiner Palmer C. Demeo Attorneys-A. T. Stratton, W. D. Palmer and Walter Sutcliff ABSTRACT: A constricted arc-discharge device having means for physically rotating the arc-tube about the longitudinal axis of the arc-tube to stabilize and maintain the constricted arc proximate the longitudinal axis of the arc tube. This device thereby avoids problems caused by arc bowing of the constricted arc-discharge. The device operates with a discharge sustaining filling comprising mercury and metallic halide and provides an extremely efficient source of visible radiation.

PATENTEU JUNZQ I9?! DRIVE MEANS INVENTORS Walter J. Burnhom 8 Robert J. Zollweg BY W ATTORNEY CONVECTIVE ARC STABILIZATION BY LAMP ROTATION CROSS-REFERENCE TO RELATED APPLICATION This application is related to concurrently filed Westinghouse Electric Corporation case No. 39,769 entitled Magnetic Stirring of Constricted Arc Lamp Vapors."

BACKGROUND OF THE INVENTION The use of metallic halide additives in high pressure mercury vapor arc-discharge devices has been a recent advance, which has allowed for increased luminous efficiency in such commercial lighting sources. Such devices when operated to provide high luminosity from what is termed a constricted arcdischarge. The are constricts to occupy only a small central core portion of the arc-tube volume when the metal halide partial pressure rises. Particularly with some metal halide fillings, and under higher power conditions of operation, when the arc-discharge is thus constricted it generally bows from the axis of the arc-tube and excessively heats one portion of the arc-tube resulting in destructive failure of the arc-tube, as well as possibly accelerating damaging chemical reaction of the operated lamp, it appears randomly directed in a vertically burning arc-tube.

The prior art includes the use of a magnetic means for interacting with a high power, horizontally burning arcdischarge device to deflect the bowed arc-discharge proximate the longitudinal axis of the arc-tube.

When an arc-discharge becomes constricted, the wall stabilization of the arc is diminished so that the arc tends to follow convection currents in the device. The constricted arc gives rise to its own inherent magnetic flux which tends to force the bowed are further from the longitudinal axis of the arc-tube.

In an investigation of convection effects upon the arcdischarge path of high pressure electrode stabilized arcdischarge devices described in Zeitshreift fur Physik; volume 122, page I, 1944, the researchers rotated a horizontally burning mercury-vapor containing arc-tube to show that the arc discharge path was not appreciably affected by the removal or at least reduction of convective effects. Of course the reason this was so was because the device was an electrode stabilized discharge device, and one wherein the discharge occupied substantially all the volume enclosed by the arc-tube. With the present generation of high power, high pressure mercury and metal halide additive devices the discharge is wall stabilized and only occupies a relatively small portion of the total volume enclosed by the arc-tube. This constricted arcdischarge tends to drift to one portion of the arc-tubewall which action impairs the performance of the device. By electrode stabilized device is meant that the arc-path between electrodes is much smaller than the arc-tube diameter. This is contrasted with the standard commercial high pressure mercury arc-discharge device which is regarded as wall stabilized, in that the arc length between electrodes is at least several times greater than the arc-tube diameter.

In the low pressure mercury discharge art grooved, or crenelated fluorescent lamp envelopes have been used to lengthen the discharge path for low pressure mercury vapor fluorescent lamps. The effect of this is to deflect the diffuse discharge and lengthen its path, and there is not a confining or directing of the discharge toward the longitudinal axis which occurs in one embodiment of the present invention.

SUMMARY OF THE INVENTION It is an object of the invention to provide an improved high efficient constricted arc-discharge device.

, discharge constituents with the wall. Such are bowing occurs in arc-tubes operating in both the vertical and horizontal position. While the bowing will be upward in a horizontally- It is a further object of the invention to stabilize the constricted are of the device away from the walls of the arc-tube to avoid destructive heating of the wall.

It is another object of the invention to provide a luminaire combination which allows for operation of the arc-discharge device incorporated therein at a very high efficiency for production of light.

These objects and others which will become apparent as the description proceeds are achieved by providing a constricted are-discharge device comprising a conventional generally tubular arc-tube with means for rotating the arc-tube about its longitudinal axis to maintain the constricted arc-discharge proximate the arc-tube longitudinal axis.

It has been discovered that the constricted arc bowing of such devices can be controlled or eliminated by rotating the arc-tube about its longitudinal axis. An improved luminous efficiency is attained because the device can be operated at higher operating temperatures without destructive heating effects both chemically and structurally occurring at the arctube walls.

It has been further discovered that by providing spiralling raised surfaces on the interior wall of a vertically operated constricted arc-discharge device that the arc can be maintained at least in the central volume of the arc-tube if not at the longitudinal axis. The arc-discharge is made to rotate in such a device as a result of the natural convection currents established in the arc-tube, and the interaction of these convection currents on the raised spiralled surfaces. The arcdischarge is thus kept in rather constant rotating motion preventing destructive heating at any one portion of the arctube.

It has been discovered that an arc-tube with spiralled raised interior wall surfaces can be used advantageously in combination with means for rotating the arc-tube about the arc-tube longitudinal axis to maintain the constricted arc-discharge proximate the longitudinal axis. The arc-tube rotation is in the same direction of the advancing spiralled surfaces to insure addition of the rotational forces on the discharge gases. This combination allows for maintaining the arc-discharge proximate the longitudinal axis at a lesser rotational speed of the arc-tube than would be possible if a conventional arc-tube with a flush interior wall surface were used.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an elevation, partly in section, of the preferred embodiment of the invention wherein the constricted arc- DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, the preferred embodiment as shown comprises an arc-tube I0 having a generally tubular envelope 12, formed of a high-temperature-resistant, radiation-transmissive material, typically quartz. The conductive lead-ins 14 are sealed through the respective ends of the envelope via press seals 16, wherein the lead-ins which are, for example, tungsten and are electrically connected to molybdenum ribbons l7 sealed within the pressed end portions.

The electrodes 18 are supported within the arc-tube 10 by the conductive lead-ins 14. The electrodes are typically coiled tungsten wound about the tungsten lead-ins. The electrodes may have an electron emissive material associated therewith to facilitate operation. An auxiliary starting electrode may also be used to facilitate starting the discharge, as is well known. The electrical conductors 20 which extend outward from the press seals are for example, molybdenum rods, which are in turn electrically connected to the outer envelope leadins 22, which are hermetically sealed through the outer envelope 24 at opposite ends thereof. The outer envelope leadins 22 are typically Kovar rods to facilitate a glass to metal hermetic seal through the outer envelope 24, which is conventional soda-lime glass or Pyrex, and which is evacuated to prevent heat losses from the arc-tube. These Kovar rods which act as the outer envelope electrical lead-ins should each be aligned to be colinear with the longitudinal axis of the arc-tube which is supported within the outer envelope. In this embodiment, the lead-ins 22 should also be relatively thick rods because the rotational force to the arc-tube is applied via one or both of these lead-ins 22. In the preferred embodiment one lead-in rod 22 is connected to a rotating means 26, which can be any conventional device for imparting rotational force via the turning ofa rod. In a very practical setup the Kovar leadins 22 each terminate in electrically conductive pivot blocks 28. The pivot blocks can be graphite or a conductive metal with graphite lubricant on the pivot surfaces. The one Kovar lead-in is mechanically connected to the rotor of an electric motor 3 2 which upon operation imparts rotational force to the Kovar lead-in to drive the arc-tube.

A typical arc-tube 10, for example, for 400 watt operation is an 18 mm. id, 20 mm. o.d. quartz member, with an arc-path between electrodes of approximately 70 mm., the envelope enclosed approximately 22 cc. The discharge sustaining filling comprises mg. of mercury, 20 mg. of Cel 20 mg. of Dyl and the arc-tube is tipped off with a 20 torrs partial pressure of readily ionizable inert starting gas, typically argon. The space between the arc-tube and the outer envelope is evacuated to minimize heat losses. Of course other additive materials can be incorporated into this high mercury pressure device as is well known in the art. The mercury must be present in an amount sufficient to establish a mercury pressure of several atmospheres during operation, and the additives which particularly give rise to the restricted arc-discharge condition include the rare-earth metal halides as disclosed by U.S. Pat. No. 3,334,261 issued Aug. l, 1967. Other metals or metallic ha lides may also be incorporated to vary the characteristic light emission.

When the arc-tube is operated in a horizontal position at about 400 watts the constricted arc-discharge bows upward and would result in destructive failure of the lamp if not corrected. By actuating the rotating means 26, the entire device including the arc-tube is caused to rotate at about 300 revolutions per minute or more, for example. The constricted arc is maintained proximate the longitudinal axis of the arc-tube, which is coincident with the rotational axis for the outer envelope.

When the arc-tube is operated in a vertical position at about 400 watts the constricted arc-discharge is unstable and waivers and bows finally in a particular direction. The rotation of the entire device by operation of the rotating means thereby rotates the arc-tube at about 600 revolutions per minute or more, for example, and the constricted arc is maintained proximate the longitudinal axis of the arc-tube.

It is also apparent that the rotating means need not be directly corrected to the lead-ins of the discharge device, and also that an embodiment can be constructed without the use of an outer envelope, In FIG. 2 the discharge device comprises simply the arc-tube, for example as set forth in FIG. 1, and conventional drive means for imparting rotational force directly to the arc-tube.

In another embodiment of the invention shown in FIG. 3 a discharge device is constructed of, for example, a 22 mm. id quartz member, which is 24 mm. o.d. The electrodes are sealed in using press seals. Then the arc-tube is evacuated via the exhaust tubulation on the side and the arc-tube is heated with a directed flame as the arc-tube is rotated and linearly moved with respect to a die to thereby provide a spiral pattern in the arc-tube wall. This is repeated to provide four spiralled splines, which are etuispaced. For a 120 mm. long arc-tube with an arc-length 0 about mm. the spirals have a spiral rate of about 1 cycle per 10 cm. of arc-tube length. The resulting plurality of spaced raised portions of the interior wall of the arc-tube are for example, three-sixteenths inch wide, and about one-eighth inch deep, i.e. the raised portions protrude inwardly approximately one-eighth inch from the normal interior wall surface. The arc-tube is then filled with discharge sustaining material, typically a charge of 30 mg. of cel;,, 30 mg. of Dyl mg. of mercury, and tipped off with argon to 20 torrs. This arc-discharge device is specifically designed for operation in a vertical position with or without rotation of the entire arc-tube. When such a device is operated at moderate halide pressure, such as provided by operating the above lamp at 400 watts the arc which constricts and tends to bow is stabilized by the provision of the spiralled splines such that the constricted arc-discharge rotates at a rate of about one turn per 2 seconds about the longitudinal axis of the arc-tube without any rotation of the arc-tube. It has been discovered that even when the arc-tube is provided with the spiralled splines, if the device is operated with a higher power input and higher metal, halide operating pressure then rotation of the arc-tube in the same direction as the advancing spiralled portions is desired to maintain the arc-discharge proximate the arc tube axis. Thus, the rotational forces add to the forces on the discharge sustaining material form any natural convection currents directed in a spiral motion by the raised surfaces. The use of the spiralled splines allows for stabilization of the constricted arc-discharge for a comparable device at a lower rotational speed of the arc-tube for vertically operated devices.

ln general the modified arc-tube formed with the spiralling raised surfaces on the interior wall of the arc-tube are of special advantage for the vertically operated arc-tube because of the greater importance in such a device of the convection current normally established. The raised surfaces of the interior wall direct this natural convection and also may improve the coupling of the arc-tube wall and the discharge gases for imparting the rotational force to these gases.

While the invention has been described with respect to a specific example of an arc-discharge device which exhibits a constricted arc-discharge upon operation, the invention is not to be limited thereto or thereby.

We claim as our invention:

1. In combination with a constricted arc-discharge device, wherein during normal operation the constricted arcdischarge will bow outward toward the wall of said device unless said bowing is controlled, the improved device and means for controlling said bowing, comprising:

a. a generally tubular,'linearly extending, radiation transmissive arc-tube with conductive lead-ins sealed through opposite ends thereof, and wherein the interior wall of said arc-tube has a plurality of inwardly projecting portions which spiral about the longitudinal axis of said arctube from one end portion to the other end of the arctube;

b. electrodes supported by said lead-ins and disposed within said arc-tube;

c. a discharge sustaining filling contained within said arctube, which during operation forms a constricted arcdischarge directed between said electrodes; and

d. means for rotating the operative arc-tube about its longitudinal axis in the same direction of the advancing spiral of said projecting portions of said arc-tube interior wall, whereby said constrictive arc-discharge is maintained proximate said longitudinal axis. 

1. In combination with a constricted arc-discharge device, wherEin during normal operation the constricted arc-discharge will bow outward toward the wall of said device unless said bowing is controlled, the improved device and means for controlling said bowing, comprising: a. a generally tubular, linearly extending, radiation transmissive arc-tube with conductive lead-ins sealed through opposite ends thereof, and wherein the interior wall of said arc-tube has a plurality of inwardly projecting portions which spiral about the longitudinal axis of said arc-tube from one end portion to the other end of the arc-tube; b. electrodes supported by said lead-ins and disposed within said arc-tube; c. a discharge sustaining filling contained within said arctube, which during operation forms a constricted arc-discharge directed between said electrodes; and d. means for rotating the operative arc-tube about its longitudinal axis in the same direction of the advancing spiral of said projecting portions of said arc-tube interior wall, whereby said constrictive arc-discharge is maintained proximate said longitudinal axis. 